This invention relates to an elastic fluid axial flow turbine or compressor. More particularly, the invention relates to a lashing structure used for the blades for such a turbine or compressor.
An elastic fluid axial flow turbine or compressor comprises a rotor having a peripheral groove and an annular row of blades having root portions disposed in the groove. A variety of blade structures are known and a variety of techniques for minimizing vibratory stresses in the blade structures have been developed.
Lashing lugs are used on longer blades to provide a tying device between blades for vibration control when the centrifugal stress becomes excessive.
A purpose of lashing blades is to reduce the bending moment in the blade and root, to raise the blade frequency in certain modes and to introduce means to tune the blade away from resonance at the running speed. A purpose of long arc lashing or shrouding is to reduce the response to high stressing modes of vibration. The shroud, whether long or short arc, offers additional benefits in acting as a rotating seal, resists strumming, and allows foreign material to pass through the row without extensive damage.
Most lashing lugs are streamlined to minimize flow disturbance which can cause performance loss. Lugs may have short spans and different tying structures such as sleeves to integrate the lug into a lashing structure have been used. Where the span of the lug is short, it is impractical to use sleeves.
Different blade constructions using lugs have been subject to failure problems.
There is the need to provide for flexibly interconnecting blades in lashing structures to minimize stress and to permit for retrofitting existing turbines and compressors.